Fair value measurements - Significant unobservable inputs (Detail) (Significant Unobservable Inputs (Level 3) [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Derivative Contract Liabilities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	$ (8,222)	$ (9,196)	$ (14,519)
Gains (losses) included in:
Earnings	(2,035)	471	3,635
Other comprehensive income	(3)
Regulatory assets and liabilities	144	(33)	47
Purchases, dispositions and settlements		533	1,664
Purchases/Issuances	(68)
Settlements	275
Transfers into (out of) Level 3	1	3	(23)
Ending Balance	(9,908)	(8,222)	(9,196)
Fixed Maturities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	801	918	639
Gains (losses) included in:
Earnings			1
Other comprehensive income	5	16	49
Purchases, dispositions and settlements		9	244
Purchases/Issuances	17
Dispositions	(39)
Transfers into (out of) Level 3		(142)	(15)
Ending Balance	784	801	918
Equity Securities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	35	304	328
Gains (losses) included in:
Earnings			4
Other comprehensive income	(13)	(8)	25
Purchases, dispositions and settlements		(1)	(8)
Transfers into (out of) Level 3		(260)	(45)
Ending Balance	22	35	304
Other Fixed Maturities and Equity Securities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	17,589	20,614	10,275
Gains (losses) included in:
Earnings		1,305
Other comprehensive income	(2,120)	(358)	4,702
Purchases, dispositions and settlements		(3,972)	5,637
Purchases/Issuances	5,000
Transfers into (out of) Level 3	(8,800)
Ending Balance	$ 11,669	$ 17,589	$ 20,614

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Purchases and issuances that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

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Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents dispositions which have taken place during the period in relation to assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

No definition available.

+ Details

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Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents amounts recorded to regulatory assets and liabilities arising from net derivative contract liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

No definition available.

+ Details

Name:	brka_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisRegulatoryAssetsAndLiabilities
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	brka_GainsLossesIncludedInAbstract
Namespace Prefix:	brka_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents [net] transfers in to and out of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant